Abstract/Summary

Analysis of the vertical velocity of ice crystals observed
with a 1.5micron Doppler lidar from a continuous sample of
stratiform ice clouds over 17 months show that the
distribution of Doppler velocity varies strongly with
temperature, with mean velocities of 0.2m/s at -40C,
increasing to 0.6m/s at -10C due to particle growth and
broadening of the size spectrum. We examine the likely
influence of crystals smaller than 60microns by forward
modelling their effect on the area-weighted fall speed, and
comparing the results to the lidar observations. The
comparison strongly suggests that the concentration of
small crystals in most clouds is much lower than measured
in-situ by some cloud droplet probes. We argue that the
discrepancy is likely due to shattering of large crystals on
the probe inlet, and that numerous small particles should
not be included in numerical weather and climate model
parameterizations.